In this article, a flip-chip assembly using a heterogeneous solder bump structure is studied. The metallurgical and shape evolution, from bump fabrication through final assembly, is presented, characterized, and discussed. Aiming for lower residual stress during flip-chip assembly, a sequentially plated bump is fabricated to ensure a ductile low Ag content solder proximate to the fragile chip back end of line (BEOL) layers while providing a separate solder portion with a high Ag content. Such a heterogeneous structure is enabled by the integration of a Ni cap barrier within the sequential electroplating process that serves to prevent Ag diffusion between the two distinct solder portions. The heterogeneous structure is shown to remain intact through the chip join operation, thereby proposing improved BEOL integrity during joint solidification. Further, the cap barrier induces a unique, pillar-like solder structure that provides the opportunity to optimize fine pitch assembly processes without the use of a stiff Cu-pillar layer. Finally, the cap barrier is shown to successfully break down using an additional reflow after underfill reinforcement, thus homogenizing the structure into a high-Ag content solder to optimize electromigration resistance.

中文翻译：

---

一种使用异质锡银凸块的新型芯片接合组件

在本文中，研究了使用异质焊料凸点结构的倒装芯片组件。从凸块制造到最终组装的冶金和形状演变都得到了介绍，表征和讨论。为了降低倒装芯片组装过程中的残余应力，制造了顺序电镀的凸块，以确保在易碎的芯片后端（BEOL）层附近形成易延展的低Ag含量焊料，同时提供单独的具有高Ag含量的焊料部分。通过在顺序电镀工艺中整合Ni帽势垒可以实现这种异质结构，该电镀工艺可防止Ag在两个不同的焊料部分之间扩散。异质结构显示通过芯片连接操作保持完整，从而提出了在联合凝固过程中改善的BEOL完整性。此外，帽盖会产生独特的柱状焊料结构，从而无需使用坚硬的铜柱层即可提供优化细间距装配工艺的机会。最后，显示出在底部填充增强之后，通过使用额外的回流，帽盖可以成功击穿，从而使结构均匀化为高Ag含量的焊料，从而优化了抗电迁移性。